Enzyme-mediated modifications of tRNA, such as 5-methylcytosine (m5C) installed by nuclear-enriched NOP2/Sun RNA methyltransferase 2 (NSUN2), play a critical role in neuronal development and function. However, our understanding of these modifications' spatial installation and biological functions remains incomplete. In this study, we demonstrate that a nucleoplasm-localized G679R NSUN2 mutant, linked to intellectual disability, diminishes NSUN2-mediated tRNA m5C in human cell lines and Drosophila. Our findings indicate that inability of G679R-NSUN2 to install m5C is primarily attributed to its reduced binding to tRNA rather than its nucleoplasmic localization. Conversely, an NSUN2 variant lacking an internal intrinsically disordered region (ΔIDR-NSUN2) can install ∼80% m5C within the nucleoplasm. Furthermore, we show that tRNA m5C levels are positively correlated to cognitive performance in Drosophila, where expressing G679R-NSUN2 leads to the most severe social behavioral deficits while expressing ΔIDR-NSUN2 results in less pronounced deficits. This work illuminates the molecular mechanism underlying G679R disease mutation in cognitive function and offers valuable insights into the significance of the cellular localization of m5C installation on tRNA for neuronal function.

中文翻译：

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NSUN2 介导的 tRNA m5C 在认知功能中的空间调节


酶介导的 tRNA 修饰，例如由富含核的 NOP2/Sun RNA 甲基转移酶 2 （NSUN2） 安装的 5-甲基胞嘧啶 （m5C），在神经元发育和功能中起关键作用。然而，我们对这些修饰的空间安装和生物功能的理解仍然不完整。在这项研究中，我们证明了与智力障碍相关的核质定位的 G679R NSUN2 突变体会减少人类细胞系和果蝇中 NSUN2 介导的 tRNA m5C。我们的研究结果表明，G679R-NSUN2 无法安装 m5C 主要是由于它与 tRNA 的结合减少，而不是其核质定位。相反，缺乏内部固有无序区 （ΔIDR-NSUN2） 的 NSUN2 变体可以在核质内安装 ∼80% m5C。此外，我们表明 tRNA m5C 水平与果蝇的认知表现呈正相关，其中表达 G679R-NSUN2 导致最严重的社会行为缺陷，而表达 ΔIDR-NSUN2 导致不太明显的缺陷。这项工作阐明了认知功能中 G679R 疾病突变的分子机制，并为 m5C 安装在 tRNA 上的细胞定位对神经元功能的重要性提供了有价值的见解。